1. Field of the Invention
This invention relates to IC devices and in particular to the formation of wiring connections of integrated circuits.
2. Description of the Prior Art
During manufacture of IC devices, the circuit elements are formed on a die, and the IC die assembly is joined to a die attach pad, typically by an epoxy adhesive. Electrical lead wires are bonded to contact points of the IC device by bonding to conductive elements or fingers and/or with the die attach pad. The lead wires in turn are coupled to external circuitry for processing data and control signals.
During the attachment of the IC die to the die attach pad, the epoxy adhesive which is made with a resin tends to bleed and flow along the surface of the pad beyond the area of joinder of the die and the pad. The flow of resin makes it difficult to properly bond the lead wires to the conductive die attach pad. With prior art processes, it is necessary to exercise stringent control of the application of the adhesive material while it is being dispensed. Furthermore, limitations on the chemical properties of the adhesive are imposed. As a result, the problem of lead wire bonding becomes time-consuming and costly.
An additional problem associated with making wire connections is the possibility of electrical shorting to the die attach pad that may occur during the bonding of the lead wires to the lead fingers, which requires extra care and testing during production. The die attach pad is made of an electrically conductive material, such as copper. The noninsulated lead wires when bonded to the lead fingers can inadvertently make contact with the conductive die attach pad, thereby creating an electrical shorting condition.
Also, during the mass production of IC devices, a multiplicity of lead wires are connected by means of automated bonding equipment to electrical contact points and bonding pads. Prior production techniques relied on an operator to designate the lead area visually, and a computer to provide alignment of the contact points that are to be bonded by bonder apparatus having capillaries for providing the bonding material. As a result of the dramatic increase in the number of lead wires which are used with IC devices and the limitations of size and space provided between the components of an IC device, the lead wires by necessity are very closely spaced, thus requiring very accurate and precise bonding in order to avoid erratic connections and electrical shorting. Therefore, during the bonding process, it is necessary to align the capillaries of the bonder appratus precisely relative to the electrical contact points on the bond pad of the die attach pad of the IC assembly.
Furthermore, with the composite rigid frame and flexible tape assembly, such as disclosed in the aforementioned copending U.S. patent application, it has been observed that when the IC device is subjected to a high temperature, such as occurs during vapor phase assembly which employs a temperature greater than 214.degree. Centigrade for example, or during heat testing, a "clam shell" effect occurs. This clam shell effect causes the lead fingers or wires of the IC assembly to bow or separate so as to distort the planar elements of the IC device, which makes the device unusable.
Another problem that may occur as a result of the production process is the delamination of the Kapton layer that secures the lead fingers of the frame and tape assembly. During manufacture of an IC device incorporating the design disclosed in the aforementioned copending patent application, an insulating film made of a material such as Kapton (a product of DuPont Corp.) is deposited on the flexible tape-like structure. The Kapton film serves to secure the thin flexible conductive leads formed with the tape-like structure, and electrically insulates the leads from each other. Kapton material is subject to becoming brittle in the presence of moisture. Also, a continuous film of Kapton has a tendency to delaminate from the tape-like structure.